Vehicle brake system and method for increasing brake pressure in a first wheel brake cylinder and limiting brake pressure in a second wheel brake cylinder of a vehicle brake system

Abstract

A vehicle brake system and method for increasing the brake pressure in a first wheel brake cylinder and for limiting the brake pressure in a second wheel brake cylinder of a vehicle brake system. The method includes increasing a first brake pressure in the first wheel brake cylinder by controlling/holding a wheel inlet valve in its open state and controlling/holding a first wheel outlet valve in its closed state, and limiting an increase of a second brake pressure in the second wheel brake cylinder during the transfer of brake fluid into the first wheel brake cylinder by controlling/holding a second wheel inlet valve in its closed state and controlling a second wheel outlet valve into its open state. The second wheel outlet valve is controlled with a pulse width-modulated signal so that during the transfer of brake fluid, the second wheel outlet valve is permanently in its open state.

What is claimed is: 
     
       1. A vehicle brake system, comprising:
 at least one brake pressure buildup device; 
 a first wheel brake cylinder having a first wheel inlet valve assigned to the first wheel brake cylinder and a first wheel outlet valve assigned to the first wheel brake cylinder, a flow of brake fluid through at least the first wheel inlet valve in its open state into the first wheel brake cylinder being brought about by an operation, brought about by driver's force and/or motorically, of the at least one brake pressure buildup device; 
 a second wheel brake cylinder having a second wheel inlet valve assigned to the second wheel brake cylinder and a second wheel outlet valve assigned to the second wheel brake cylinder, a flow of brake fluid through at least the second wheel inlet valve in its open state into the second wheel brake cylinder being brought about by the operation of the at least one brake pressure buildup device; and 
 a control device by which, during the operation of the at least one brake pressure buildup device, the first wheel inlet valve can be controlled into its open state, the first wheel outlet valve can be controlled into its closed state, the second wheel inlet valve can be controlled into its closed state, and the second wheel outlet valve can be controlled at least at times into its open state, so that a first brake pressure in the first wheel brake cylinder can be increased while an increase of a second brake pressure in the second wheel brake cylinder is simultaneously at least limitable; 
 wherein the control device is configured to, during the operation of the at least one brake pressure buildup device, control the second wheel outlet valve with a pulse width-modulated signal in such a way that the second wheel outlet valve controlled by the pulse width-modulated signal is permanently in its open state. 
 
     
     
       2. The vehicle brake system as recited in  claim 1 , wherein the control device is configured to, during the operation of the at least one brake pressure buildup device, hold a current strength maximum and a duty cycle of the pulse width-modulated signal low enough that the current strength maximum and the duty cycle are just sufficient to hold the second wheel outlet valve controlled by the pulse width-modulated signal permanently in its open state. 
     
     
       3. The vehicle brake system as recited in  claim 2 , wherein the control device is configured to, during the operation of the at least one brake pressure buildup device, hold the current strength maximum and the duty cycle of the pulse width-modulated signal low enough that the pulse width-modulated signal has a current strength, averaged over time, of less than 0.5 A. 
     
     
       4. The vehicle brake system as recited in  claim 1 , wherein the control device includes at least one flyback diode and is configured to output the pulse width-modulated signal to the second wheel outlet valve using the flyback diode. 
     
     
       5. The vehicle brake system as recited in  claim 1 , further comprising:
 a master brake cylinder: (i) to which a brake actuating element is connectable or is connected, and/or (ii) before which a brake booster is pre-positioned; 
 wherein at least one pump and/or at least one motorized plunger device is the at least one brake pressure buildup device. 
 
     
     
       6. The vehicle brake system as recited in  claim 1 , wherein the first wheel brake cylinder with its assigned first wheel inlet valve and its assigned first wheel outlet valve, and the second wheel brake cylinder with its assigned second wheel inlet valve and its assigned second wheel outlet valve, are situated in a common brake circuit of the vehicle brake system. 
     
     
       7. A method for increasing a brake pressure in a first wheel brake cylinder and for limiting a brake pressure in a second wheel brake cylinder of a vehicle brake system, the method comprising the following steps:
 increasing a first brake pressure in the first wheel brake cylinder by, during an operation brought about by a driver's force and/or motorically of at least one brake pressure buildup device, controlling and/or holding a first wheel inlet valve assigned to the first wheel brake cylinder in its open state, and controlling and/or holding a first wheel outlet valve assigned to the first wheel brake cylinder in its closed state, so that brake fluid is transferred through at least the first wheel inlet valve in its open state into the first wheel brake cylinder by the operation of the at least one brake pressure buildup; 
 at least limiting an increase of a second brake pressure in the second wheel brake cylinder during the transfer of brake fluid into the first wheel brake cylinder by controlling and/or holding a second wheel inlet valve assigned to the second wheel brake cylinder in its closed state, and controlling a second wheel outlet valve, assigned to the second wheel brake cylinder, at least at times into its open state; and 
 controlling the second wheel outlet valve, during the transfer of brake fluid into the first wheel brake cylinder, with a pulse width-modulated signal that brings about that during the transfer of brake fluid into the first wheel brake cylinder, the second wheel outlet valve is permanently in its open state. 
 
     
     
       8. The method as recited in  claim 7 , wherein a current strength maximum and a duty cycle of the pulse width-modulated signal is kept so low during the transfer of brake fluid into the first wheel brake cylinder, the current strength maximum and the duty cycle are just sufficient to bring about that the second wheel outlet valve is permanently in its open state during the transfer of brake fluid into the first wheel brake cylinder. 
     
     
       9. The method as recited in  claim 8 , wherein the current strength maximum and the duty cycle of the pulse width-modulated signal are kept so low during the transfer of brake fluid into the first wheel brake cylinder that the pulse width-modulated signal has a current strength, averaged over time, of less than 0.5 A. 
     
     
       10. The method as recited in  claim 7 , wherein the pulse width-modulated signal is produced and output to the second wheel outlet valve by a flyback diode.